Observation of Superluminal Behaviors in Wave Propagation

Abstract

The possibility of observing superluminal behavior in the propagation of localized microwaves over distances of tens of wavelengths is experimentally demonstrated. These types of waves, better than the evanescent modes of tunneling, can contribute to answering the question on the luminal limit of the signal velocity.

Causal explanation for observed superluminal behavior of microwave propagation in free space

“…Fourier theory implies that a signal with compact support in the frequency domain is unlimited in the time domain, i.e., has no fronts and as such it is impossible to define a front velocity for it and only the group velocity has physical meaning. Following this reasoning, we cannot endorse the point of view of [18] which seems also the one adopted in [1], simply because it implies the existence of wave packets in the time range ∞ < < ∞ − t , i.e., even before the antenna was turned on. The concepts presented above, although of fundamental character, are unfortunately not well known as they should be.…”

“…In this note we make some comments on a recent paper by Mugnai, Ranfagni and Ruggieri [1] claiming the observation of superluminal behavior in microwave propagation for long distances in air. Our comments are of theoretical nature and about possible explanations for the measured effect.…”

“…From the theoretical point of view, we start by analyzing the following statement quoted in [1] and attributed to [2]: "Yet, there is no formal proof, based on Maxwell equations that no electromagnetic wave packet can travel faster than the speed of light." First of all we note that every physical wave (satisfying Maxwell equations) produced by a physical device of finite dimension (antenna) must necessarily have a beginning (possibly) an end in time, say at t T = − and 0 t = .…”

“…After these necessary preliminaries, we can now present specific criticisms to the contents of [1]. Recall that we can generate solutions of Maxwell equations with the Hertz potential method [9,16].…”

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In this paper we present a theoretical analysis of an experiment byIn this note we make some comments on a recent paper by Mugnai, Ranfagni and Ruggieri [1] claiming the observation of superluminal behavior in microwave propagation for long distances in air. Our comments are of theoretical nature and about possible explanations for the measured effect.

From the theoretical point of view, we start by analyzing the following statement quoted in [1] and attributed to [2]: "Yet, there is no formal proof, based on Maxwell equations that no electromagnetic wave packet can travel faster than the speed of light."

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